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Student Chapter • American Association of Equine Practitioners New York State College of Veterinary Medicine • Cornell University PUNKIES, PIN WORMS, AND OTHER PARASITES: A Look at Parasite Induced Skin Diseases By Luba Drouin, '87 Equine skin diseases can interfere with the horse's appearance, comfort, and ability to perform to capacity. This can be very annoying to the horse, the owner and the veterinarian. Parasites such as the horse stomach worm, lice and pinworms can manifest themselves as skin disease. This article deals with several parasite-induced skin diseases (dermatoses), how they occur, and their diagnosis, treatment and prevention. Cutaneous Habronemiasis More commonly known as summer sores, cutaneous habronemiasis is a skin disease associated with the horse stomach worms, Habronema muscae and Habronema majus, and Draschia magastoma, that have a symbiotic relationship with the house- and stable-fly. The normal destination they usually die. The horse's female stomach worm produces larvae that are immune system mounts an inflammatory passed in the equine host's feces and ingested response to the larvae in the surrounding tissue by the larvae of house or stable flies which live leading to the formation of an itchy, yellowish in manure deposits. The worm larvae then take ulcerated lesion and granulation tissue. up residence within the fly larvae. The cycle is completed when the fly larvae hatch into adult Treatment of these lesions can require flies and deposit the stomach worm larvae surgical removal when there is excessive around a horse's mouth. The horse swallows the granulation. Early in the process, as well as in stomach worm larvae that pass to the stomach areas where surgical excision is difficult, where they mature into adults. corticosteroids (cortisone-like drugs) are used to quiet down the immune system and hence Summer sores occur when these worm reduce the inflamatory response and itch. larvae are attached to areas of damaged skin on Recently, ivermectin has been reported to be the legs, around the eyes, and the prepuce. The beneficial in the treatment of habronemiasis. flies deposit the larvae of the stomach worm in Due to the locations of these granulomatous the damaged skin and the larvae penetrate the lesions, cryosurgery has proven to be more dermis, but since they are far from their effective than conventional surgical techniques. EQUINE B o u n d s Prevention requires strict fly control on the horse and in its environment. Wounds should receive immediate attention, be bandaged when possible and kept clean to discourage the flies from landing on the site. Paste worming with ivermectin will also decrease the adult parasite population in the stomach and decrease the number of larvae available to the fly population. Onchocerciasis Onchocerciasis is another parasite- induced equine dermatosis. Onchocerca cervicalis is a worm that lives in the ligamentum nuchae or thick, fibrous, supporting structure of the neck muscles in horses. The adult worms produce microfilariae that migrate through the connective tissue to the skin of the belly midline, face, and eyes. When these microfilaria die, the body's inflammatory response produces swelling and redness followed by ulceration. The horse may experience itching, oozing and crusting of lesions, resulting treatment. Since the actual damage in the eye in loss of hair and skin pigment. If the as well as in the skin is caused by the body's microfilaria are migrating through the eye inflammatory response to the foreign antigen, when they die this can result in multiple eye the microfilariae, the severity of the outcome problems. can be decreased by treating with corticosteroids prior to treating with Most horses have some Onchocerca ivermectin. Corticosteroids will decrease the microfilariae in their connective tissue. Some inflammatory response and itching and lessen horses however seem to form an allergic skin damage. response against the outer coat of the microfilariae. These horses have an Culicoides Hypersensitivity overwhelming allergic inflammatory reaction resulting in the cutaneous damage mentioned Culicoides hypersensitivity has a seasonal above. occurence associated with the culicoides gnats (also called punkies and no-see-ums) during Onchocerchiasis can be treated summer months. The disease is caused by a systemically with ivermectin. Since the disease hypersensitivity (allergic) reaction to the saliva is believed to be due to the continuous death of of these gnats. They usually feed on the the microfilariae, killing large numbers of dorsum of the horse producing a pruritic microfilariae at once will give the horse a dermatitis that leads to excoriation, crusting, break from the disease. But horseowners should scaling and alopecia and erythema on the exercise caution in the use of ivermectin if the forehead, neck, withers, shoulders, rump, and horse is having eye problems along with the skin base of the tail. Many of these lesions are problems. Ivermectin will kill the microfilariae secondary to the self trauma inflicted by migrating through the eye and this could result rubbing, especially in the tail and mane areas. in serious eye problems. A veterinarian should Mosquito or black fly saliva may also affect examine the eyes prior to ivermectin some horses in the same way. EQUINE B o u n d s There may be a hereditary predisposition in that some families of horses may be more sensitive to gnat, black fly and mosquito bites. Treatment involves intensive insect control. These almost microscopic insects are found in areas of high humidity and around water. They like to feed in the evening hours, so pasturing horses in the evening will actually expose them to these pests. If this is a serious problem on the farm it would be helpful to stable horses from dusk to dawn. Diligent application of repellents may help lessen the sensitivity. Mosquito screens are not effective because gnats readily pass through them. Corticosteroids are often needed to control severe itching. Oxyurias associated with itching. Lice are usually found on the neck around the mane, but can be Caused by Oxyuris equi or pin worms, present anywhere. oxyurias leads to an anal itching that results in constant tail rubbing. The adult worms live in Because most infections occur through the large bowel of the horse, but the female close contact, affected animals should be migrates out to the anus and deposits her eggs isolated to prevent spread of the parasites. in the anal area. The itching caused by the Horse lice are very host specific and will not presence of the pinworm eggs leads to tail live on other species, however, they can live rubbing producing erosions, redness and broken without a host for up to 2 weeks so it is possible hairs around the base of the tail, symptoms to spread lice infection through contaminated much like that of culicoides hypersensitivity. brushes and tack. Application of water-based, However, finding eggs of the pin worm around organophosphate insecticides is the approved the anus will help identify oxyuriasis. To find treatment, but administering a water bath the eggs of Oxyuris equi place scotch tape on during the cold winter months is not appealing the anal region and examine it under a to man or beast. Thus insecticidal powders are miscroscope. commonly used. This may be why it is difficult to rid the animal of lice in winter. In the Lice summer, the problem will usually resolve. Lice infestation usually occurs during the Perhaps the most difficult aspect of skin winter months. This is probably due to the diseases, especially those that are parasite- horses' long hair coats, close animal contact, induced, is finding the cause. But with and even the stress of cold weather. persistence it is possible to get to the root of the itch, treat it, and work to prevent it in the There are two types of lice: biting lice, future. Damalina equi, and sucking lice, Haematopinus asini. Biting lice usually cause itching and hair loss and excoriation secondary to the itching. Luba Drouin, student editor of this issue of Sucking lice may cause anemia due to the Equine Rounds, is beginning her final year in blood loss during feeding and hair damage the DVM program. EQUINE TtOUNDS LUMPS & BUMPS maximal size. Earlier removal may result in recurrence and stimulation of growth. Many By Corine Farewell '89 chemical treatments and wart vaccines have been advocated, but their value is disputed. Sarcoids Horses are subject to a variety of conditions which result in the formation of Sarcoids are the most common neoplasm neoplasms on the skin surface. Neoplasia can in horses. They are fibrous, locally aggressive be defined as an uncontrolled multiplication of tumors which have a predilection for the skin of cells which form a mass or growth. Although the limbs, head, neck and chest, but may occur some of these are of little consequence to the on any body surface. Similar to the papilloma, well-being of the animal, others may be life- sarcoids are also induced by a virus and only threatening. Some of the more common occasionally regress spontaneously. neoplastic "lumps and bumps" on horses are: Sarcoids are classified into four types: Papilloma verrucous, fibroblastic, mixed fibroblastic and verrucous and occult. Verrucous sarcoids Commonly referred to as "warts," these resemble a wart and are recognized as a growth small growths are caused by a virus which has a on or above the skin level. The verrucous type predilection for the muzzle, lips and eyelids. In may be confused with a papilloma at the onset severe cases, the warts may extend back to the of growth. When the verrucous sarcoid is jowl and even on the chest and front legs. injured, it may grow quickly into a fibrous (fibroblastic) sarcoid or a mixed At the onset of the disease, the warts are fibroblastic/verrucous sarcoid.

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